This application is not referenced in any microfiche appendix.
In general, the present invention is directed to crude oil refining. In particular, the present invention is directed to a system and method to advance the efficiency of severe thermal cracking, or coking, by effecting and stabilizing the temperature of coker feedstock, or process fluid, preceding its introduction to a coker charge heater.
The present invention can be best understood and appreciated by undertaking a brief review of the crude oil distillation process, and most particularly, the critical role coker charge heaters play within that process.
In its unrefined state, crude oil is of little use. In essence, crude oil (a.k.a. hydrocarbon) is a complex chemical compound consisting of numerous elements and impurities. Such impurities can include, but are not limited to sulfur, oxygen, nitrogen and various metals that must be removed during the refining process.
Refining is the separation and reformation of a complex chemical compound into desired hydrocarbon products. Such product separation is possible as each of the hundreds of hydrocarbons comprising crude oil possess an individual boiling point. During refining, or distillation, crude oil feedstock temperature is raised to a point where boiling begins (a.k.a. xe2x80x9cinitial boiling point, or xe2x80x9cIBPxe2x80x9d) and continues as the temperature is increased. As the boiling temperature increases, the butane and lighter fraction of crude oil are first distilled. Such distillation begins at IBP and terminates slightly below 100xc2x0 F. The fractions boiling through this range are represented and referred to as the xe2x80x9cbutanes and lighter cut.xe2x80x9d The next fraction, or cut, begins slightly under 100xc2x0 F. and terminates at approximately 220xc2x0 F. This fraction is represented and referred to as straight run gasoline. Then, beginning at 220xc2x0 F. and continuing to about 320xc2x0 F. the Naphtha cut occurs, and is followed by the kerosene and gas/oil cuts, occurring between 320xc2x0 F. and 400xc2x0 F., and 450xc2x0 F. to 800xc2x0 F., respectfully. A term-of-art xe2x80x9cresidue cutxe2x80x9d includes everything boiling above 800xc2x0 F.
The residue cut possesses comparatively large volumes of heavy materials and two fundamental processes are employed to convert appreciable amounts of such residuals to lighter materialsxe2x80x94thermal cracking and delayed coking. While thermal-cracking may be properly considered xe2x80x9cthe use of heat to split heavy hydrocarbon into its lighter constituent components,xe2x80x9d delayed coking should be considered xe2x80x9csevere thermal crackingxe2x80x9d and occurs within a coke drum after a coker feedstock has been heated in an apparatus referred to as a coking heater, or xe2x80x9cdelayed coker charge heater.xe2x80x9d An improved delayed coker charge heater and process serve as the focus of the instant invention.
In the present art, fresh feed is preheated by preheat exchangers exclusively, prior to introducing such feed to combination tower for processing. Fresh feed of a cold variety is first introduced to the refining process from tankage, while hot feed is introduced to the refining process from a vacuum distillation unit, or units. As preheat exchangers foul from use, their operating efficiency diminishes over time. Less efficient preheat exchangers, in turn, occasion temperature variances in fresh feed prior to its introduction to a combination tower. Coke drum overhead temperatures and flow rates also vary, as do heavy gas only (HGO) quench rates, both contributing to the instability of residuals temperature at the bottom of a combination tower. Especially large temperature savings occur when switching from a hot coke drum to a cold coke drum. Consequently, a combination tower""s bottom temperature varies greatly based upon input from the afore stated sources.
The utilization of coker pre-heaters are well known in the art. As intended, the purpose of a coker pre-heater was to preheat process fluid, or coker feedstock, when the unit was designed without an effluent exchanger train or with a minimally configured feed/effluent exchanger train. In such instances, temperature control and firing rates are based on pre-heater outlet temperature. The present art clearly lacks innovative consideration to maintain, stabilize, and control combination tower xe2x80x9cbottomsxe2x80x9d temperature. In providing for such maintenance, stabilization and control, the present invention introduces a novel means by which xe2x80x9ctemperature stabilizedxe2x80x9d combination tower bottoms can be introduced to a coker charge heaters, and thus, maintain and stabilize the firing rates of such heaters.
Hence, given the deficiencies of the present art and improvements afforded by the instant invention, what is needed is an improved system and method to effect and control temperature of coker process fluid, in advance of introducing such fluid to a coker charge heater.
The present invention provides for an improved method and article of manufacture for greatly improving upon coker charge heater performance and longevity. By maintaining and controlling the combination tower bottom""s temperature, the absorbed duty rate and firing rate of a coker charge heater can be held nearly constant. Maintaining a nearly constant coker firing rate prevents the tubes in the charge heater from overheating during inlet temperature swings associated with the prior art. Of equal or greater importance is that preventing tubes from overheating also reduces the rate of internal coker tube fouling and therefore increases the run length between decoking (cleaning), further extending tube life of the process coil.
Consequently, it is an objective of the instant invention to increase process fluid temperature subsequent to pre-heat exchanger processing, and prior to the introduction of such feed to combination tower processing.
It is a further object of the instant invention to serve as a substitution for feed/effluent exchangers by increasing fresh feed exchanger outlet temperatures beyond those temperatures achievable utilizing such exchangers, prior to the introduction of such feed to combination tower processing.
An additional objective of the instant invention is to increase coker charge heater inlet temperatures such that a reduction in firing rates and duty load swings may be realized.
A further object of the instant invention is to provide a means by which process fluid lines and combination tower temperatures may be maintained at an operational level during coke drum swings from one drum to the other drum and during unit cold start ups, thus reducing xe2x80x9cstart upxe2x80x9d time associated with the present art and greatly reducing or eliminating over firing of the coker charge heater.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed description to follow, taken in conjunction with the accompanying drawings wherein like parts are designated by like reference numerals.
FIG. 1 is an illustration of a typical hydrocarbon refinery configuration as represented in the present art.
FIG. 2 is an illustration of the invention""s preferred embodiment.
FIG. 3 illustrates an alternative embodiment of the instant invention.
FIG. 4 illustrates an additional alternative embodiment of the instant invention.
FIG. 5 illustrates a further alternative embodiment of the instant invention.
FIG. 6 is a logic flow diagram of the invention""s preferred methodology in effectuating and controlling a nearly constant coker charge heater process fluid inlet temperature.